The invention relates to a method of amplifying an input signal having a DC component and an AC component.
The invention applies more particularly to integrated circuits for processing audio signals. It therefore relates particularly to transmission and reception circuits for wireless telephones.
These circuits generally use a device for optimizing the bandwidth and improving the signal to noise ratio of the demodulated signal. This device consists of two units: a compressor for the transmission part and an amplifier also called expander for the reception part. These two units are very sensitive to offset voltages. Thus these two units are in general coupled to a capacitance which serves as a high-pass filter, so that any offset introduced by previous units is canceled out. This implementation has the advantage of canceling out the offset but costs an external capacitor and two connection pads.
One aim of the invention is to make it possible to reduce the sensitivity of the amplifier to voltage offset without using such a coupling with a capacitor.
A method of amplifying an input signal having a DC component and an AC component is characterized according to the invention in that it includes the following steps:
comparing the input signal with a reference value,
generating an intermediate signal by subtracting from the input signal a so-called correction signal resulting from said comparison,
rectifying the intermediate signal,
evaluating a mean value of the rectified intermediate signal,
multiplying the input signal by said mean value.
The method according to the invention proposes in fact a compromise which takes account of the change over time in the input signal in order to eliminate an offset voltage. The value of the input signal is compared at each moment with a reference value and this comparison causes the generation of a correction current. The invention makes it possible to avoid using a capacitor which is external and consequently expensive to use. The invention also makes it possible to avoid the multiplication of connection pads which are sources of error during manufacture.
Moreover, the invention presents a supplementary and important advantage of squelch reduction for the amplification according to the method of the invention. This advantage is particularly interesting for audio reception applications.
In one of its applications, the invention also relates to a device including modules for performing the functions according to the invention. More generally, the present invention can advantageously be implemented in an apparatus, for example a wireless telephone, whose reception chain comprises elements liable to introduce an offset within the processing of the signal received.